Piezo-electric-crystal control system



Nov. 23 ,1926. 1,608,048

A. H. TAYLOR PIEZO ELECTRIC CRYSTAL CONTROL SYSTEM Filed Jan. 23, 1926 2 Sheets-Sheet l {2/ I I I I I I I P-Q INVENTOR. fl 56 1*! E ]& /023 BY %M i A TTURNEY Nov. 23 1926. 1,608,048

A. H. TAYLOR PIEZO ELECTRIC CRYSTAL CONTROL SYSTEM Filed Jan. 25, 1926 2 Sheets-Sheet z INVENTOR.

A TTORNEY Patented Na. z3, 192s.

ALBERT n. TAYLOR, or wasnmcron,

' aamo, me, or new YORK, N.

rrso STATES.

DISTRICT OF COLUMBIA, .ABSIGINOIB IO wnpw Y., A COB?ORATION. 0F DELAWAEP.

' PIEZO-ELECTBIC-CRYSTAL CONTROL SYSTEM.

Application filed January 23, 1926. Serial No. 88,406.

My invention relates broadly to piezo electric crystal control circuits, and more particularly to a protective circuit arrangement for preventing the fracture or break down of piezo electric crystals under conditions of over-loading.

One of the objects of my invention is to provide a piezo electric crystal control system with means for preventing the fracture or break down of piezo electric crystals under conditions of excessive currents in the circuits of an electron tube oscillating system which the piezo electric crystal is arranged to control.

Another object of my invention is to provide an electron tube piezo electric crystal controlled oscillator system where the piezo electric crystal is'protected against excessive radio frequency currents by a current limit relay circuit arranged to break the oscillator circuit upon increase of the radio frequency current beyond a safe value.

Still another object of my invention is to provide an automatic protective system for piezo electric crystals by which rise in current through the piezo electric crystal operates to break the plate circuit for preventing increase of the current through the piezoelectric crystal to a point where the crystal may be strained or ultimately destroyed.

My invention will be more clearly under-.

stood by reference to the accompanying drawings, wherein:

Figure 1 shows diagrammatically an electron tube oscillator with a circuit for protecting the piezo electric crystal control in accordance with the principles of my invention; Fig. 2 illustrates a modified circuit arrangementfor the protection of the piezo electric crystal circuit which connects with the electron tube oscillator; and Fig. 3 illustrates still another modified arrangement of piezo electric crystal controlled and oscillator circuit having an electron tube protective system operating upon increase in radio frequency current beyond a predetermined value for breaking the, electron tube oscillator circuit.

In the operation of piezo electric crystal control circuits for radio transmitters conditions have arisen in which the piezo electric crystal has been fractured or broken destroying the operation of the crystal. I have observed that under continuous operation the crystal becomes hot, due, among" satisfactory.' Brushing can be very dam-' aging long before it can be seen, and overheating under this condition, takes place so rapidly that the crystal would be destroyed before the discovered. Attempt has been ma e m over-cheated condition could radio. transmitter operation to so adjust the number of turns in the inductance in the plate circuit of the piezo electric crystal controlled oscillator that the energy in the plate circuit, and therefore the output radio frequencyenergy, is held down. In spite of this precaution, however, piezoelectric crystals have been shattered and broken into pieces in oscillator circuits due to excessive rise in current in the piezo electric crystal control circuit. Theoretical considerations indicate that the thing which determines the condition of the crystal more than anything else, is the amount of radio frequency current supplied to the grid of the tube which is obliged to pass through the crystal or rather through that capacity determined by the top and bottom plates of the crystal with the crystal itself as an intervening dielectric. By placing a radio frequency milliammeter in the grid circuit of the piezo electric crystal controlled oscillator either above or below the piezo electric crystal, the rise in current through the piezo electric crystal may be observed. A position next to the grid electrode of the oscillator, that is, above the piezo electric crystal in the input circuit of the oscillator is preferable if the meter can be somounted as to offer little capacity between the case of the meter and the earth, otherwise it is befier to insulate the lower crystal contact plate andplace the meter in the lower position. It has now been definitely determined that for normal crystal operation, the permissible grid -.current-at radio frequencies which in a way passes through the crystal, has a v'ery; defifrequency. I ,of protecting the crystal by increasing the nite upper limit be end which heating will ra idly develop an the crystal structure is he. le to be flawed, fractured, or otherwise damaged. This permissible radiofrequency current throu h the crystal is directly proportional to t e area 0 the crystal and in general u to 4000 kcs., increases wlth the e fallacy vof the arrangement late turns and settings until the output l alls ofi will 'be readily understood. Investigations have shown that when the plate turns are increased (thereb reducin power I input and power output) t e radio requen- I of the oscillator is relatively unimportant.

, reach the maximum safe limit.

cy grid currents increase, thereby subjecting the c stal actually to a greater straln with a' lig t load, than it would have had The latter tells the operator nothing whatever'a'bout the crystal althou h it does give warning when the tube' itse f isfgoing to overheat, but at the present time crystals are far more valuable than tubes; at least 7 watt tubes. The circuit is started out on a low voltage, generally 220 volts on the plate, and the plate turns are adjusted down-' ward until a reasonably 1good circuit adj ustment is obtained with t e radio frequency grid mills at a low value. Then the voltage is raised until the radio frequency grid mills This is practically the reverse of the former method of adjusting crystal circuits, because instead of starting out with'a large number of plate turns, thus holding back the plate (D. O.) milliamperes, the plate turns are started low, holding back the radio frequency grid milliamperes. The use of the grid milliammeter permits. observations to be .made with safet with 50 watt tubes, whereas prior to this, it has been thought that it was not entirely safe to try to operate a 50 watt tube with crystal control unless intervening amplifiers were employed. A great many crystals were fractured in the attempt to accomplish direct operation of the crystal in the input circuit of ahigh frequency tube. With my circuit arrangement, however, it is nowv entirely possible to operate 5.0 watt tubes not always to full output, but to much higher power, than can be expected with a 7 watt tube provided the circuit is adjusted with reference to the grid radio frequency milliammeter and the output radio freqpency meter with little or no reference to t e plate current. I have found that the radio frequency grid milliamperes is a direct function of the grid to plate capacit and and thereby opening the plate circuit of the oscillator for maintaining the through the piezo electric crystal below a safe limit. I may also utilize the increase in the drop across a resistance in series with the piezo electric crystal for controlling the operation of an electron tube circuit and actuating a current limit relay in the plate circuit thereof when the current through the piezoelectric crystal tends to rise beyond a safe limit.

Referring to the drawings in more detail, reference character 1 indicates an electron tube having filament, grid and plate elec trodes 1', 1 and 1. The filamentor cathode 1 is heated from source 2 under control of rheostat 3. An input circuit 4 is provided connected across the grid and filament electrodes, and an output circuit 5 is provided connected across the plate and filament electrodes. The input circuit 4 includes a choke coil 6 and a source of potential 7 connected across the input circuit in such manner that the piezo electric crystal 8 may be operated in the input circuit 4 under substantially no load. The contact plates 9 and 10 are provided between which the piezo electric crystal 8 is mounted. The radio frequency milliammeter 11 is connected in series with the piezo electric crystal 8 as shown. The indicator 12'may be entirely insulated from the mechanism of the milliammeter 11 and arranged to close an electrical circuit with contact 14 set at a point along the scale of the milliammeter at which the current may increase to a predetermined limit below a value that may be destructive to the piezo electric crystal 8. A relay hav ing a, spring, ten'sioned armature 16 and a contact; member 18 is provided in the output circuit 5 of the electron tube oscillator. The relay includes an electromagnetic winding 15 which is connected in a circuit 23 including the indicator arm 12, adjustable contact 14 and battery 17 The output circuit 5 of theelectron tube oscillator includes inductance 19, variable capacity 20, high potential source 21, shunting condenser 22 and the current rise in grid current beyond a given limit I necessary meters. piezo electric crystal fects of excessive currents.

functions to control. the oscillations developed in the electron tube oscillator system and will continue to maintain the oscilla tions therein at constant frequency solong as the current through said piezo electric crystal remains below a predetermined limit and a safe value.

Upon rise of current through piezo electric crystal 8 the indicator arm 12. completes connection with contact 14 energizing the relay winding 15 and opens the plate circuit of the oscillator, thus .automatically protecting the piezo electric crystal against excessive current.

In Fig. 2 I have illustrated a rectifier 26 in circuit with the piezo electric crystal 8 whereby the" direct current component proportional tothe radio frequency current through piezo electric crystal 8 energizes winding 25 with which is associated the spring tensioned armature 27 which normally connects with the back contact 28. The

plate circuit of the electron tube oscillator extends along the connections represented at 24 and is completed through armature- 27 and contact 28. Upon excessive rise of current through the piezo electric crystal 8, the

plate circuit of the oscillator is thereby automatically interrupted and the piezoelectric crystal protected against the destructive eff As represented in Fig. 3 a resistance 29 may be connected in series with the piezo electric crystal 8 and an electron tube 30 having filament; grid and plate electrodes 30, 30 and 30 provided and arranged to be controlled by the drop across resistance 29. The cathode 30 is heated from battery system 31 under control of rheostat 32. The out ut circuit of electron tube 30 includes hig potential source 35and relay Winding 3 shunted by condenser 33. A spring tensioned armature 27 is arranged to be actuated b relay winding 34 with a contact 28 norma ly closed by the spring tensioned armature 27 for completing the plate circuit of the oscillator in a mannersimilar to that represented in Fig. 2. The operating characteristics of tube 30 may be so controlled by a proper value of grid potential represented invention are intended other than those imposed by the scope of the appended claims.

.What I claim and desire to secure by Letters'Patent of the UnitedStates is as follows:

1. A piezo electric crystal control system.

comprising in combination an electron tube oscillator, a. piezoelectric cr stal for controlling oscillations generate by said elec- "tron-tube oscillator, and means for opening the circuit of said electron tube oscillator upon increase in current through said piezo electric crystal .beyond a predetermined limit.

2. A piezo electric crystal control system comprising in combination an electron tube oscillator, a piezo electric crystal for con: trolling the operation of said electron tube oscillator, and means connected in series with said piezo electric crystal for opening. the circuit of said electron tube oscillator when the current through said piezo electric crys- 8 injury to said piezo electric crystal due to rise of current in said input circuit beyond a predetermined limit.

4. A piezo electric crystal control system comprising in combination with an electron tube oscillator having input and output circuits, a piezo electric crystal connected in said input circuit, a relay interposed in said output circuit, and means connectedin series with said piezo electric crystal in. said input circuit for actuating the relay in said output circuit when the current through said piezo electric crystal exceeds a predetermined value.

5. A iezo electric crystal control circuit comprising in combination an electron tube oscillator, input and output circuits connected with said oscillator, a piezo electric crystal arranged in said input circuit, a relay interposed in said output circuit including a spring tensioned armature and a con tact member, and a winding for said relay arranged to be energized upon increase in current through said piezo electric crystal for moving said armature away from said contact and breaking said output circuit for preventing rise of current through said piezo electric crystal. beyond a predeter mined value.

6. In an electron tube oscillator s stem, a space current discharge device inc uding an evacuated envelope containing a plurality of electrodes, circuits interconnecting said electrodes, a piezo electric device for controlling the operation of said circuits said space current disc device,

and a current limit relay actuated by er:- cessive current through said plezo electrlc device for interruptin the operatlon of 7. In combination, a space current discharge device comprising an evacuated envelope containing a plurality-ofelectrodes, a piezo electric device for controllmg the operation of said space current discharge device and automatic means responsive to increase in current through said piezo electric device for rendering said space ischarge device inoperativef 8. In combination, a space current dis charge device comprising an evacuated-en-' of electrodes, a piezo elecve ope, a plurality tric device for normally controlling the operation of said space current discharge and magnetic means responsive to an increase in current through said piezo electric device for rendering said space dis charge device inoperative.

9. In combination, a space current discharge device comprising an evacuated envelope, a plurality of electrodes, a piezo electric device for normally controlling the operation of said .space current discharge device, and a current limit electromagnetic relay device responsive to increases in current through said piezo electric device for rendering said space discharge device inoperative.

10. An electron discharge device comprising an envelope, cathode, anode and control arge device. a

filament and plate electrodes, in ut and out put circuits interconnecting sai electrodes, a piezo electric device connected in said input circuit, a rectifying device disposed in series with said iezo e ectric device, a relay connected in sai output circuit and connections between said rectifying device and said relay whereby an increase in current through said piezo electric device actuates said relay for opening said output circuit.

12. In a system for generating high fre-' quency electrical oscillations the combination of an electron tube having grid, filament and plate electrodes, input and output circuits interconnecting said electrodes, :1 piezo electric device connected in said input circuit for controlling'the operation of said electron tube, and a rectifying device connected in series with said piezo electric device and having means whereby an in-. crease in current beyond a' redetermined limit throngh said piezo e ectric device operates to open said output circuit for rendering said eectron tube inoperative.

ALBERT H. TAYLOR. 

